Receivers are used in a wide variety of communication systems. A communication system typically includes front-end circuitry that processes incoming signals and provides them to additional receiver circuitry. In particular, a radio frequency signal is often transmitted through an air interface and received at an antenna. The signal may then be actively or passively filtered to select a frequency band of interest. A communication system may have a single frequency band of interest, or it may have multiple frequency bands of interest that can be received. For example, with respect to cellular telephone communication systems, different frequency bands are used by cellular networks depending upon the geographic location and type of the cellular network in operation, and cellular handsets are often configured to operate in multiple bands. Band selection is accomplished in many communication systems with a filter circuit, such as a surface acoustic wave filter (SAW), but also can be accomplished by other means. It is noted that to accomplish an optimal trade-off of out-of-band attenuation, desired passband characteristics, overall performance, size, and cost, this filter circuitry is often tuned specifically to the desired band of interest. The band-selected signal may then pass through input match circuitry to maximize the signal power or signal voltage to the receiver inputs. This match circuitry can be located in any preceding stage to the receiver inputs. The signal is then provided to frequency band specific inputs of the receiver where the first receiver stage commonly includes a frequency-band-specific low noise amplifier (LNA). As with the filter circuitry, it is noted that receiver inputs are often tuned to the frequency range or band of interest to accomplish an optimal trade-off of out-of-band attenuation, desired passband characteristics, gain, noise, overall performance, size, current consumption, and cost. It is further noted that there may be frequency-band-specific local oscillator signals provided to a mixing stage after low noise amplification is completed to down-convert the received signal to a desired intermediate frequency or to baseband for subsequent demodulation and digital processing.
Many communication systems also include transmit path circuitry. As such, transceiver (receiver plus transmitter) integrated circuits are often utilized in a wide variety of communication systems. The addition of the transmitter affects the front-end circuitry by often requiring the addition of an antenna switch module (ASM) that includes transmit filtering to select between either receive or transmit operation in communication systems where the receive and transmit operation are not concurrent or otherwise active at the same time. It is noted that the ASM may be exchanged for a duplexer that can provide isolation between the receive and transmit paths while combining the transmit and receive paths at the antenna in communication systems with concurrent receive and transmit operations. Combinations of these concurrent and non-concurrent communication systems may also be made, and the front-end circuitry for such combined systems can include both an ASM and a duplexer. It is also noted that additional functions may be implemented in the front-end network, if desired.
It is also common for the different functions and blocks within the front-end system to be combined together in a modularized package for use in communication systems that are directed to commonly used sets of frequency bands. Some of the different modularized package combinations of interest that are commonly encountered in communication systems, such as cellular telephone handsets, include front-end modules (FEMs) that combine ASMs and any combination of available SAW filters, include SAW filterbanks that integrate any combination of available SAW filters, and include modules that combine SAW filterbanks with associated matching networks. It is noted, however, that these examples should not be considered as limiting, and it is recognized that other combinations, modules and arrangements can be provided, if desired. In short, a wide variety of modules can be provided that combine antenna switches (such as ASMs and duplexers), filterbanks (such as SAW filterbanks), and additional circuitry (such as input matching networks). As indicated above, these different module combinations can be implemented for use with selected frequency bands, as desired. It should also be noted that when considering FEMs, filterbanks, and receivers/transceivers for different communication systems and the number of vendors that provide these products, while there may be several frequency bands available to implement, it is rare to find a communication standard that specifies the ordering of the frequency bands as they are defined and placed in the package.
In some communications environments, different communication systems utilize different frequency bands for device communications. For example, with respect to GSM/GPRS/EDGE cellular telephone communication systems, different frequency bands are used depending upon the geographic location and type of the cell network in operation. In the United States of America, the frequency bands utilized are currently the 850 MHz (GSM) and 1900 MHz (PCS) bands. In Europe and Asia, the frequency bands utilized are currently the 900 MHz (E-GSM) and 1800 MHz (DCS) bands. A quad-band handset typically refers to a cell phone that operates in all four of these frequency bands. A triple-band handset typically refers to one that operates in three of these frequency bands. And a dual-band handset typically refers to one that operates in two of these frequency bands.
While quad-band cell phones are available, the bulk of the cellular phone handset market currently ships as dual-band or triple-band handsets. The band combinations selected for these dual and triple band handsets are often different among the various handset manufacturers depending upon the markets being targeted by those manufacturers. Considering that there are two low bands (GSM, E-GSM), two high bands (DCS, PCS), and at least one of each is typically chosen for a handset, there are eight available dual and triple band combinations that could be selected by the handset manufacturers (GSMIDCS, GSM/PCS, E-GSMIDCS, E-GSM/PCS, GSMIDCS/PCS, E-GSM!DCSIPCS, GSM/E-GSMIDCS, and GSMIE-GSMIPCS). As such, for flexibility, a handset manufacturer will typically require quad-band support from the transceiver integrated circuit (IC) it uses for its handsets. Using this transceiver IC, a manufacturer will then make a variety of handsets with different dual-band or triple-band combinations depending upon frequency bands it selects for markets it targets to minimize cost overhead. This approach, therefore, requires financial and labor resource allocation with respect to each different handset design for schematic generation, printed circuit board generation, certification, and inventory management.
In short, it is often desirable for communication systems to operate in multiple frequency bands. It is also often desirable for communication system manufacturers to make one communication system for a first set of frequency bands, a second communication system for a second set frequency bands, and so on. With prior solutions, however, each new set of frequency bands requires specific front-end circuitry, specific PCB routing, and/or different variations of receiver/transceiver integrated circuits in order to allow the different communication systems to work.